Protect your gems from being stolen by "good" heroes in this tower defense game. Overlord, you have all the power of orcs, undead and demons. Try to annihilate the enemies before they grab a gem, but even if they do, you'll have a chance to annihilate them on their way back and you'll save the gem.
Use mouse (hold SHIFT to build multiple towers or cast multiple spells). The game has a bult-in tutorial.